Christian Wolmar is a journalist and broadcaster who specializes in transportation.  A former transportation correspondent for The Independent newspaper, he is a frequent guest on TV and radio shows, appearing most recently in the railway documentary “Ian Hislop: Trains That Changed the World.” The author of twenty books, his volumes on railway history include: The Great Railway Revolution: The History of Trains in America; Blood, Iron and Gold: How the Railroads Transformed the World; and The Subterranean Railway: How the London Underground Was Built and How it Changed the City Forever.